The present invention relates to an engine starter having a planet reduction gear mechanism and, particularly, to a mounting structure of a planet gear arm and a roller pin of the reduction gear mechanism.
FIG. 3 is a cross section of a main portion of a conventional engine starter having planet reduction gear mechanism, in which a reference numeral 1 depicts an armature of a d.c. motor and 2 depicts a drive shaft which is integral with the armature 1 and has one end formed with a solar gear 2a of the planet reduction gear mechanism. A reference numeral 3 depicts an annular field magnetic pole of the d.c. motor, which is affixed to an inner peripheral surface of an annular yoke 4. An inner gear 6 is fitted to a bracket 5. Planet gears 7 each supported by a roller pin 8 implanted on a planet gear arm 9 formed integrally with a driven shaft 10 (FIG. 4) are arranged between the solar gear 2a and the inner gear 6. The planet gear arm 9 has holes 9a into which the roller pins 8 are pressure-inserted to complete the implantation. A packing 11 is provided between the bracket 5 and the inner gear 6 and a steel ball is provided between a front end of the drive shaft 2 and a rear end of the driven shaft 9.
In such starter having an output power rate of, for example, 0.7 to 2.2 KW, a thickness t of the planet gear arm 9, on which the roller pins are to be implanted, must be 4 to 8 mm, a diameter of the roller pin 8 must be 6 to 8 mm and a force for pulling-out the roller pin 8 from the planet gear arm 9 must be more than 200 Kg depending upon the size of the starter and the module of the gear to be used. Therefore, the size of the hole 9a of the planet gear arm 9 must be very precise. Further, since the roller pin 8 is inserted into the hole 9a from one side thereof under high pressure, a periphery of the hole 9a in the other side tends to be deformed as shown by a reference numeral 13 in FIG. 5. Such deformed portion 13 which may contact with a wall of the inner gear 6 has been removed by cutting away. Alternatively, a gap between the planet gear arm 9 and the inner gear 6 has been made large enough to avoid such contact. However, either of such solutions requires an increased number of manufacturing steps or an increase of size of the starter and thus it has been difficult to make the starter compact and light-weight.